A friendly thing to do would be develop a script that took the google results, checked with whois for abuse address and sent emails. Of course that could also end up with one being sent to jail for a long time.
Isn't it required that there's an abuse@ address to comply with RFCs. So take Google link list, do a reverse domain lookup, uniq, and email abuse@$(those domains).
If someone else later does something bad with the publicly accessible printer and there's a witch hunt for the responsible party, and the only lead they have is that you emailed them about the possibility in advance...then they'll go after you, even though you were just trying to do a good thing.
And if you're expecting the victim / police / legal system to understand that, technically speaking, it could have literally been anyone with an Internet connection...Or if you think that your good intentions and lack of criminal record mean that the most you'll get is a slap on the wrist even if they think your email "proves" that you did it...you're quite naive, especially given all the recent coverage of Aaron Swartz.
I should note that this isn't unique to computers, by the way. You should also never leave a note on an unlocked car saying "hey, noticed your car was unlocked --signed XYZ".